Because the structure of scooter is simple and convenient for carrying, scooter has become many people's recreational sports and even travel tools. However, when the surface of the road is rugged, it will be uncomfortable for the user due to the impact of the vertical force. If there are large gaps in the road, the safety of user will be threatened. Additionally, the life expectancy of the scooter will be shorten. As a result, a suspension device between the wheels and the frame has been incorporated into some scooter designs to resolve the above problems. The existing designs of the suspension system are open and exposed, and their suspension effect is accomplished by the mutual movement of the parts of the suspension device by transforming the impact load. However, in such designs, the objects can be easily drawn into the exposed suspension device, impeding the relative motion of the parts in the suspension device, resulting in inadequate or no suspension effect by the suspension device.